This invention relates to work transfer devices which transfer articles or workpieces in a vertical sense.
Manufacturing operations, particularly mass production operations, typically utilize powered transfer devices for advancing workpieces in process along the manufacturing line. Often the workpieces must be vertically transferred as a part of the work flow, either upwardly or downwardly. In the case of downward transfer, gravity may be used in some situations. Other downward transfers, and of course upward transfers, require a powered transfer device.
Heretofore, devices such as elevating chain conveyors have been used when vertical transfer is required. These devices comprise one or more endless chains operating on vertically spaced sprockets with one or more of the sprockets being driven by a source of power. Buckets or platforms are connected to the chains at selected spacings, and the workpieces are carried by the buckets or platforms. The chains are operated either continuously or by indexing. Because an endless chain itself revolves 360.degree. as it travels once around its path of travel, special connections of the buckets or platforms to the chains may be required if 360.degree. revolution of the buckets or platforms themselves is deemed objectionable. While chain type devices are generally recognized to be cost-competitive as far as initial sales price is concerned, special features, such as these special connections for example, contribute to their cost. There are the further costs which are not recognized in the sales price, and these are the operational costs involved with use of such chain type devices. The problems of chain type devices are well-known to those familiar with them and it is these which constitute the operational costs. Chain type devices are also not readily adaptable to different elevating heights. Yet, despite the disadvantages which are seemingly inherent in chain type devices, they continue to enjoy popularity due to the competitiveness of their initial sales price.
In other instances, other types of vertical transfer devices are used. An example of another type is a power cylinder elevator where a power cylinder is disposed at the bottom a stack of articles. The stack is confined within a vertical guide, and pivotally mounted stops are mounted on the guide at vertically spaced locations. When the cylinder is operated to push the stack upwardly, the stops pivot out of the way allowing the stack to advance upwardly. Once an article clears a stop, the stop pivots back into the path of the stack so that the article which has just cleared it cannot fall back. When the cylinder retracts, the stops support the articles in their new positions, and a new article is loaded at the bottom of the stack. When the cylinder is again advanced, it engages the newly loaded article to elevate the stack. The problem with this type of device is that the stack must always be full if the entire stack is to be elevated; in other words, an article at the most downstream point will not be advanced or unloaded, unless the underlying stack is full. Another disadvantage with this type of device is that only certain types of articles are suitable for this type of transfer. It is also impossible to use it for lowering articles.
The present invention is directed to a new and improved work transfer device for vertically transferring workpieces or articles. Not only does the invention avoid the problems which are seemingly inherent in chain type devices, but it is also surprisingly cost-competitive with them. The invention may be used with various types of workpieces, and it may be operated bi-directionally (i.e., either upwardly or downwardly) by merely reversing the direction of the drive. It can be adapted to operate over large distances without major modification, a feat which can be accomplished by a chain type device, if at all, only through more substantial modifications. Thus, the invention is seen to represent a significant improvement over presently available devices.
Briefly, the present invention, in its preferred embodiment, comprises a plurality of vertically spaced stations supported on a base. Workpieces are progressively advanced from station to station by a vertically disposed transfer bar. The transfer bar has work holders at vertical spacings corresponding to the spacing of the stations. A drive for the transfer bar is adjacent the stations and causes the transfer bar to repeatedly execute an operating cycle whereby the workpieces are advanced one station per cycle. Unique motion is imparted to the transfer bar comprising (1) an initial vertical upward component of motion wherein the work holders on the transfer bar lift the workpieces off the stations followed by, (2) a first horizontal component of motion to vertically clear the workpieces of the stations and (3) a second horizontal component of motion to vertically realign the workpieces with the stations including (4) during the time between the beginning of the first horizontal component of motion and the end of the second horizontal component of motion a vertical component of motion which vertically advances the workpieces so that the end of the second horizontal component of motion the workpieces are directly over their next stations followed by, (5) a downward vertical component of motion wherein the workpieces are deposited on these next stations, followed by, (6) a third horizontal component of motion to vertically clear the transfer bar work holders of the workpieces and (7) a fourth horizontal component of motion to vertically realign the transfer bar work holders with the workpieces including (8) during the time between the beginning of the third horizontal component of motion and the end of the fourth horizontal component of motion a vertical component of motion which vertically retracts the transfer bar so that at the end of the fourth horizontal component of motion the transfer bar is in position where it is poised to begin the initial vertical upward component of motion of the next operating cycle.
When the direction of advance is upward, the vertical component of motion which occurs between the beginning of the first horizontal component of motion and the end of the second horizontal component of motion is executed concurrently with the first horizontal component of motion so that the resultant motion is in a straight line with the workpieces vertically advancing and clearing the stations. The second horizontal component of motion is executed without any accompanying vertical motion to bring the workpieces into vertical realignment with and overlying the stations. The downward vertical component of motion is then executed depositing the workpieces on the stations. The vertical component of motion which occurs between the beginning of the third horizontal component of motion and the end of the fourth horizontal component of motion is executed concurrently with the third horizontal component of motion so that the resultant motion is in a straight line with the empty workholders on the transfer bar vertically retracting and clearing the workpieces which are supported on the stations. The fourth horizontal component of motion is executed without any accompanying vertical motion to bring the transfer bar work holders into vertical realignment with and underlying the stations so that the transfer bar work holders are poised to pick up the workpieces during the initial vertical upward component of motion of the next operating cycle.
When the direction of advance is downward, the first horizontal component of motion is executed without any accompanying vertical motion whereby the workpieces supported on the transfer bar work holders vertically clear the stations. The vertical component of motion which occurs between the beginning of the first horizontal component of motion and the end of the second horizontal component of motion is executed concurrently with the second horizontal component of motion so that the resultant motion is in a straight line which transfers the workpieces into vertical realignment with and overlying the stations. The ensuing downward vertical component of motion deposits the workpieces on the next stations and is sufficient to clear the transfer bar work holders of the workpieces after the workpieces have been deposited on the stations. The third horizontal component of motion is executed without any accompanying vertical motion to vertically clear the transfer bar work holders of the stations and workpieces. The vertical component of motion which occurs between the beginning of the third horizontal component of motion and the end of the fourth horizontal component of motion is executed concurrently with the fourth horizontal component of motion so that the resultant motion is in a straight line terminating with the transfer bar work holders poised directly beneath the workpieces in position to lift the workpieces from the stations upon the first vertical upward component of motion of the next cycle.
In the preferred embodiment, motion is imparted to the transfer bar by means of a mechanical drive. The mechanical drive comprises horizontally disposed members extending from the drive and connected to the transfer bar. Horizontal and vertical components of motion are generated and transmitted to the transfer bar through at least one of these members. The vertical component of motion is developed from a vertical barrel cam and the horizontal components of motion from a horizontal barrel cam. The two barrel cams are coaxial and are driven in unison with 360.degree. rotation of the barrel cams corresponding to one complete operating cycle of the transfer bar. Crank and bellcrank mechanisms are operatively associated with the transmission of motion from the barrel cams to the transfer bar. In particular, horizontal motion is derived from the horizontal barrel cam by means of plural bellcranks connected together by a drag link. This provides what may be considered as a four-bar parallelogram linkage support of the transfer bar and this type of a support allows the length of the transfer bar to be extended vertically a substantial distance so as to accommodate increased vertical height. In other words, the only adaptation that is required to a machine of the invention in many instances is simply to increase the length of the transfer bar. This is in contrast to a chain type drive where it is necessary to reposition sprockets and to increase the length of the chains; a task which is considerably more difficult than is the case with the present invention.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.